This proposal addresses the role of adenosine receptors in regulation of new blood vessel growth. Our research suggests that adenosine receptors induce synthesis of angiogenic factors in hypoxic tissues and promote homing of endothelial progenitor cells to the ischemic heart. The goal of the current application is to study the role of adenosine A2B receptors in regulation of cell proliferation and modulation of pro-angiogenic properties of cardiac and bone marrow stem/progenitor cells. Due to their low affinity to adenosine, A2B receptors are likely to remain silent under physiological conditions, but are engaged during ischemic injury when extracellular adenosine levels are increased. Based on our preliminary observations in Sca1-positive cardiac stem cells, we hypothesize that activation of A2B receptors stimulates stem cell proliferation and increases VEGF production via beta-catenin/Tcf signaling axis of the canonical Wnt pathway. If our hypothesis is correct, this would imply that the A2B receptor may regulate paracrine functions and survival of therapeutically administered cells. We will test this hypothesis in Specific Aim 1 by examining the role of adenosine receptors and associated intracellular pathways in regulation of beta-catenin/Tcf signaling axis in isolated Sca1-positive cardiac stem cells. In Specific Aim 2, we will evaluate the role of adenosine A2B receptors in Sca1-positive cardiac stem cell proliferation and VEGF production in vivo. In Specific Aim 3, we will determine the role of this receptor subtype in survival and angiogenic properties of bone marrow stem/progenitor cells transplanted into the heart. Finally, in Specific Aim 4 we will determine the contribution of adenosine A2B receptors to the therapeutic effects of cardiac and bone marrow stem cells in an acute myocardial infarction model. Elucidation of the role of adenosine receptors in these cells will not only contribute to our understanding of molecular mechanisms of neovascularization, but may also result in improvement of cell-based therapies being developed to treat ischemic diseases.